Propylene-based resin has heretofore been used in various fields as an industrial material for automotive components, components of household electric appliances, etc.
For example, JP-A 62-256837 discloses, as a polypropylene resin molded article excellent in mechanical characteristics, temperature characteristics and hardness, a polypropylene resin molded article produced by thermally treating, at a temperature within a range of from 155 to 170° C., a molded article obtained by molding a composition comprising a polypropylene resin and a nucleating agent.
JP-A 62-283111 discloses, as a propylene copolymer excellent in mechanical characteristics, temperature characteristics and hardness, a propylene copolymer produced by thermally treating a propylene copolymer having an α-olefin unit content of from 0.5% by weight to 10% by weight and a melt flow rate of from 0.05 g/10 rain to 50 g/10 min over a temperature range from (Tm−10° C.) to (Tm+5° C.), where Tm represents the melting point of the propylene copolymer.
WO 01/81074 discloses, as a method for improving the rigidity and toughness of an ethylene-propylene polymer composition, a method comprising heating the polymer composition for a period of from 1 hour to 100 hours at a temperature within a range of from 75° C. to 150° C.
The polypropylene resin molded articles disclosed in the documents are not satisfactory in rigidity or impact strength and therefore their improvement are demanded.